1. Field of the Invention
The present invention relates to a heat exchanger for heat transfer between a first fluid and a second fluid, comprising: a block for the separate and heat-exchanging guiding of the first and second fluid, and a fluid connection for the first fluid; the block which has a housing with a chamber, through which the second fluid flows, and a block closure element, also called a base, for separating the chamber and the fluid connection, and/or an interior space of the fluid connection. The invention relates further to an exhaust gas recirculation system, a charge air supply system, and use of the heat exchanger for an internal combustion engine of a motor vehicle.
2. Description of the Background Art
Heat exchangers have the task of cooling a hot first fluid with the aid of a colder second fluid, so that the first fluid, particularly an exhaust gas or charge air, can be mixed into the intake air for an internal combustion machine, for example, an engine. The second fluid is usually made as a coolant, which can be removed from the cooling circuit of the internal combustion engine. Basically, to increase the thermodynamic efficiency, the aim is that the cooling occurs to as low a temperature level as possible. It is known that the concept of cooled exhaust gas recirculation or cooled charge air can be used to reduce pollutants, particularly nitrous oxides, in the exhaust gas. Owing to the increased basic requirements for a heat exchanger and the operating mode of modern internal combustion engines, it has turned out that a heat exchanger is exposed increasingly to greater mechanical stresses because of thermal loads. This relates particularly to the area of the fluid connection and of the block closure element, particularly in the area of entry of the first fluid. In this area, the relatively hot first fluid and the cooler second fluid are separated by the block closure element closely adjacent in a relatively narrow space. The stresses caused there by different temperatures in the heat exchanger usually have a direct effect on the lifetime of the heat exchanger.
This problem has proven to be increasingly serious, particularly in modern diesel engines. In addition, however, the problem of thermal stresses within the scope of increased power densities and increased dynamics during engine operation proved to be important in other modernized engine concepts as well, e.g., also in gasoline engines. It turned out that increasing inlet pressures and temperatures with simultaneously increased cooling rates, or temperature differences, are to be sought in a heat exchanger, as limited a pressure drop as possible to be achieved simultaneously. This is to be realized increasingly with relatively inexpensive materials and basically with saving of materials and with consideration of narrower design spaces.
These circumstances intensify the problem of thermally induced stress, particularly at joining seams, primarily in adjacent components of different thickness, as can be the case in the aforementioned fluid connection and the block closure element, as well as the housing. The block closure element is basically used for separating the relatively hot first fluid from the cooler second fluid.
Designs according to the conventional art provide that the fluid connection is fixed to the block closure element. In this type of design, relatively thin guiding channels for the first fluid and relatively thick components, such as the housing and fluid connection, are fixed close together in the area of or on the block closure element. Thus, very different measures have been proposed in designs of this type to reduce the thermally induced stresses in the area of the block closure element. These include structural measures for realizing the block closure element, or if applicable for realizing a unit comprising a block closure element, housing, and fluid connection, as well as highly different types of joining and attachment of the block closure element and the components fixed to the block closure element. Depending on the employed material, welded and/or soldered and/or glued connections are used in this area.
It turned out that the increased requirements for component strength and lifetime of a heat exchanger, exposed to increased thermal stress, cannot always be met in a satisfactory way by designs according to the conventional art. The aforementioned area of the connection of the fluid connection, block closure element, and housing is particularly problematic.